1. Field of the Invention (Technical Field)
The Pseudo-Plane Wave Generator invention relates to measuring electronic circuit responses of large objects and more particularly to a distributed electronic and mechanical apparatus comprised of one or more stations of a radiating array that can generate an electromagnetic environment suitable for measurement of the circuit response of electrically large objects to free field, plane wave environments within the confines of a volume, like an anechoic chamber, that normally would not permit such a measurement due to the large distances normally associated with the creation of a true plane wave environment. The invention applies to a broad range of applications that utilize wavelike phenomena represented by the linear superposition principle, including, but not limited to sonar, audio, and optics applications.
2. Background Art
To measure the electronic circuit response of large objects (many wavelengths in extent at the frequency of operation) subjected to a free field, transverse electromagnetic (not guided wave), plane wave environment at RF and electromagnetic frequencies, (typically in the 20 MHZ-20 GHz frequency range) one has in the past been required to conduct measurements at outdoor ranges. For electrically small objects a plane wave-like environment can be established with a compact range, and measurements can be made in an electromagnetic anechoic chamber. However, it is difficult, or impossible, within the confines of an anechoic chamber, to test the response and behavior of electronic equipment housed within an electrically large object, and coupled to the plane wave environment via multiple distributed, apertures and/or wire penetrations. Disclosed is a unique way to generate a pseudo-plane wave electromagnetic environment within a small, confined region. Whereas a true plane wave would bathe the region occupied by the object under test (OUT) housing electronic equipment uniformly, the Pseudo-Plane Wave Generator generates an electromagnetic field that approximates a plane wave field only over limited extents of one or more continuous or discontinuous volumes or regions occupied in whole or in part by the OUT. The locations and extents of these regions are specified by an operator, and the Plane Wave Generator""s operating system software conducts an optimization utilizing a Genetic Algorithm procedure to determine the amplitude and phase of electrical signals that excite each radiating element of each transmitting station. The resulting electromagnetic environment, being the summation or superposition of all radiating elements of the Plane Wave Generator, will stimulate the sensors of a test object in a manner that mimics its response to a free field, plane wave environment.
U.S. Pat. No. 5,721,554 to Hall, discloses a technique for generating a simulated angle of arrival for testing a multi-wavelength sensor aperture. The device consists of three to five transmitting antennas. The excitation of each radiating antenna is determined via an analytical technique. The resulting electromagnetic environment will simulate a free field, plane wave environment over a region that is 10 wavelengths long in a single dimension, and located 100 feet to 200 feet from the device. The device is capable of creating an electromagnetic environment that simulates a free field, one dimensional, plane wave arriving at a maximum deviation angle of 2-degrees relative to a line between the device and the object under test.
U.S. Pat. No. 5,247,843 to Bryan, discloses a system and technique for generating an electromagnetic environment such as would be seen by a moving object. The system utilizes a collection of feed horns in combination with a reflector or lens, and a 3 degree of freedom positioner to create an electromagnetic environment that approximates a free field plane wave incident from an arbitrary angle. The device relates to apparatus and method for using compact ranges to simulate electromagnetic environments for computer controlled test systems to measure the electronic response of small (just a few wavelengths in extent) moving objects, i.e., a missile, to a free field plane wave electromagnetic environment.
U.S. Pat. No. 3,719,812 to Bishop, discloses a system and technique for generating a receiver input signal that would be created by a plurality of simultaneously operating radio frequency transmitters having time-varying transmission parameters and having time-varying relative positions with respect to the receiver. The input signal is comprised of a plurality signals, and combined in a circuit to generate the receiver input signal. The disclosed system does not rely on the use of a radiated field.
U.S. Pat. No. 5,339,087 to Minarik, discloses a system and technique for emulating plane wave propagation from multiple transmitting antennas to measure the response of an array processor in both a static and dynamic manner. Different transmitters radiate signals into free space and are coupled to the array processor via a receiving antenna to create a simulated signal by the wavefront simulator. The simulated signal is supplied directly to the electrical circuits. The system does not rely on the use of a radiated field.
U.S. Pat. No. 6,056,780 to Aubry, discloses a method for positioning electromagnetic sensors in an array in order to optimize a certain antenna property. Using a Genetic Algorithm optimizing procedure, the method determines the optimum locations and relative placements of a finite number of antennas for the purpose of maximizing a particular characteristic, like maximizing antenna gain in a particular direction.
U.S. Pat. No. 5,719,794 to Altshuler, discloses a process whereby the design of a wire antenna can be automated and optimized. Given a representation of the solution space (i.e., number of straight wires allowed in the solution) and one or more desired operating characteristics, (i.e., operating bandwidth, gain, direction of maximum antenna gain) the procedure will synthesize an antenna design. The evaluation of a particular candidate antenna design is accomplished by rigorously computing its electrical properties.
None of these devices, however, disclose generating an electromagnetic environment with multiple plane wave-like regions located in multiple, possibly disconnected, user specified positions, and with the capability to produce two, and three dimensional field distributions. In addition, these devices do not teach the use of an arbitrary number of electromagnetic transmitting stations that can be distributed about an object under test, almost arbitrarily. Also, these devices are not configured to produce a near field plane-wave-like electromagnetic environment by the utilization of a Genetic Algorithm.
The generation of plane wave electromagnetic environments at RF and electrical frequencies (typically in the 20 MHZ-20 GHz frequency range) for testing the response and behavior of electronic equipment can be difficult, or impossible, within the confines of an anechoic chamber. Disclosed is a unique way to generate pseudo-plane waves in confined environments. Whereas a true plane wave would bathe the region occupied by the electronic equipment with power density and phase that are uniform over an unbounded planar surface, the Pseudo-Plane Wave Generator generates an electromagnetic field that approximates a plane wave field only over limited extents of continuous or discontinuous volumes or regions occupied by the OUT housing electronic equipment.
The Pseudo-Plane Wave Generator is comprised of various control circuits, radiating elements, and an algorithmic procedure utilizing a Genetic Algorithm optimization procedure that determines near-optimum array excitation vectors from specifications (frequency, position, etc.) input to a computer by an operator. The optimization result is then translated by the computer to electrical commands to electrical control circuits that can control the amplitude and phase of electrical signals used to drive radiating antennas. The superposition of the fields radiated by the multiple antennas results in an excellent approximation to the desired electromagnetic environment at the specified physical locations. These specified locations must be in the radiating near field of the transmitting station(s), that is, within a distance of approximately 2D2/xcex, from the transmitter with D the largest overall dimension of the transmitter array or OUT, whichever is larger.
The preferable single transmitting station of the Pseudo-Plane Wave Generator comprises a 16-element transmitting station, with an operating frequency in 20 MHZ-20 GHz range. We select 1 GHz frequency for illustration purposes. The control circuit comprises a means to control amplitude and phase of the radiated circuit. The Pseudo-Plane Wave Generator can include the use of 1 or more transmitting stations, with more or less than 16 elements comprising each transmitting station.
A primary object of the present invention is to provide a capability to measure the electronic circuit responses to an electromagnetic plane wave environment of a large object that is coupled to the exterior environment via distributed, small apertures and/or wire penetrations.
A second object of the present invention is to provide a capability to create an arbitrary electromagnetic environment within a region to measure the electromagnetic response and/or behavior of an object, such as an antenna, placed within the region.
A third object of the present invention is to provide a capability to find the magnitude and phase of each radiating element of the Pseudo-Plane Wave Generator from geometrical information, and by utilizing a Genetic Algorithm to find a near-optimum solution of a complex optimization problem.
A fourth object of the present invention is to provide a capability to create a predefined, desired (often, but not necessarily, planar-like) field distribution over one or more connected or disconnected areas. That is, although the previous discussions have involved creation of plane-wave-like fields to provide a capability for testing in the radiating near field of the transmitting stations, the present invention encompasses the generation of any predefined field distribution.
A fifth object of the present invention is to provide a capability for the generation of any predefined, desired (often, but not necessarily, planar-like) shaped phasefronts and amplitude types for the broad range of wave phenomena that are well characterized by linear superposition principles. These include, but are not limited to, electromagnetic, audio, optical, seismic, and sonar applications.
A primary advantage of the present invention is that it allows the measurement of the electromagnetic response and/or behavior of an electrically large object (extends many wavelengths along its largest dimension) within the confines of volumes where previously such measurements were impossible to make.
A second advantage of the present invention is that it allows the creation of an electromagnetic environment with specific properties needed to conduct a particular measurement.
A third advantage of the present invention is that it is extensible and expandable. The Pseudo-Plane Wave Generator can be easily augmented with additional transmitting stations, providing greater capability and more flexibility in the number of plane-wave-like regions calculated, and an increase in the fidelity of the plane-wave-like properties within their regions.
Where more than one transmitting station comprises the planewave generator, the dimension xe2x80x9cDxe2x80x9d in 2D2/xcex is now largest dimension of total system.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.